Formation of Cr Nanocrystals for Nonvolatile Memory Applications

We fabricated metal-oxide-semiconductor (MOS) structures containing Cr nanocrystals (NCs) as a charge trapping layer and investigated their memory characteristics. Symmetric and large flat-band voltage shifts were observed for forward and reverse gate voltage sweeps due to the charging/discharging of Cr NCs. Memory capacitors with Cr NCs of 4 - 8 nm in size showed the best memory characteristics, with a memory window of similar to 7.3 V for a sweep voltage range of +/- 7 V and a stored electron charge density of similar to 3.1 x 10(12)/cm(2). Smaller Cr NCs seemed to suffer from surface oxidation of the NCs. Compared with higher work function Pt, Cr NC memory capacitor, with an intermediate work function, showed a faster program/erase speed and better charge retention. We discuss how the work function of a metal NC affects the memory characteristics.